Fluorine-containing surfactants have been utilized as emulsifiers in producing polymers by emulsion polymerization and as coagulation stabilizers. Recently, development works have been made actively to reduce the fluorine-containing surfactant content in products. For example, the reverse osmosis membrane method (cf. e.g. Patent Document 1) and the ion exchange membrane method (cf. e.g. Patent Document 2) have been investigated as the methods of recovering the fluorine-containing surfactant in aqueous solutions. However, these membrane methods encounter a problem from the cost viewpoint since when used for the treatment of fluorine-containing surfactant solutions containing an uncoagulated polymer, the membranes are readily contaminated and membrane exchange is required each time.
Fluorine-containing surfactants have been utilized in emulsion polymerization of fluoropolymers, among others. The technology of purifying a tetrafluoroethylene resin powder (trademark: Lubron L-2) as a fluoropolymer with carbon dioxide in a supercritical condition has been proposed (cf. e.g. Patent Document 3). However, Lubron L-2 is a product reduced in molecular weight by irradiation with γ rays, and it is considered that no fluorine-containing surfactant may remain therein.
Polymers can be obtained in the form of aqueous dispersions by emulsion polymerization, for instance, and the technique for coagulation for producing powders thereof by adding a coagulation aid such as an electrolyte or a water-soluble organic solvent to the aqueous dispersions and stirring the resulting mixtures has been established and used for long.
On the occasion of fluorine-containing surfactant recovery or polymer coagulation, substantially polymer-free aqueous solutions containing a fluorine-containing surfactant are formed. These aqueous solutions have so far been discarded as industrial waste water. From the waste disposal treatment viewpoint, however, it is desirable that the fluorine-containing surfactant content be reduced.    Patent Document 1: Japanese Kokai Publication 2002-58966    Patent Document 2: Japanese Kokai Publication 2002-59160    Patent Document 3: Japanese Kokai Publication H07-134435    (Example Section)